Jersey prop James Ellershaw has been involved in what the club are describing as a "serious car accident" in his home town of Luton.
The 29-year-old signed from Old Albanians in the summer and also made one appearance for Saracens in the Premiership last season.
Jersey say the prop has suffered "multiple injuries".
"Everyone at Jersey RFC has been shocked and saddened by the news," said chairman Bill Dempsey.
"Our thoughts are with him and his family.
"We are anxiously awaiting more news on his progress, and hoping that the next bulletins are positive ones - we wish James a swift and full recovery."